The present invention is related to a flame retardant thermoplastic elastomer film composition for use in forming films for use in automotive interiors, wallcoverings, upholstery, advertising films, and tenting materials, which employs a maleated polypropylene to improve the physical properties such as melt processing, tear strength, and tensile properties while allowing the incorporation of more flame retardant into the composition.
Thermoplastic elastomer compositions are known for their rubbery characteristics and frequently are used to modify polyolefin compositions, such as polyethylene and polypropylene. Often these thermoplastic elastomers are copolymers of ethylene and olefins, such as butene or octene, which are produced with metallocene or Kaminsky catalysts. One example of a polyolefin/thermoplastic elastomer blends are U.S. Pat. No. 5,998,524 to Srinivasan et al (and related U.S. Pat. Nos.5,763,534; 5,773,515; 5,703,629; and 5,985,971), which disclose a composition having a majority of polyolefin, modified by the elastomeric component. Another example is U.S. Pat. No. 5,834,381 to Roe et al, which discloses a rubber (i.e., an elastomer) modified polypropylene which is 10 mils in thickness, is flame retardant, and is laminated to a scrim for use as auto security shades or covers. U.S. Pat. No. 5,576,374 to Betso et al discloses a polyolefin combined with a thermoplastic elastomer for use in filled composites and to make molded parts. U.S. Pat. No. 5,750,600 to Nozokido et al discloses an oil-extended olefin thermoplastic elastomer composition for use in skins of interior automotive trim. The Nozokido composition has a majority of elastomer (i.e., 50 to 70%) and 30 to 50% of a combination of polypropylene resins having different crystal melting points and is used to make sheets having a thickness of 0.25 to 0.45 mm. As noted in Nozokido, when the elastomer content is higher than 70% by weight, problems in manufacturing are encountered and vacuum forming suffers.
Maleated polypropylenes are substituted polyolefins which have been used to copolymerize with thermoplastic elastomers or as compatabilizers for thermoplastic elastomers. For example, U.S. Pat. Nos. 5,912,296, 5,910,530, and 5,905,116, to Wang, et al., disclose a process for preparing an oil extended graft copolymer compositions that are composed of a maleated polypropylene grafted to a functionalized thermoplastic elastomer. However, no prior art has taught maleated polypropylene as compatibilizing the flame retardants and fillers, enhancing the physical properties and allowing higher levels of flame retardant and filler while being processed. U.S. Pat. No. 5,910,540, to Takahashi, discloses a thermoplastic elastomer composition that exhibits favorable heat fusion properties, and a maleated polyolefin, such as a maleated polypropylene, is added to the composition as a compatibilizer. However, Takahashi is distinguishable from the present invention because Takahashi teaches the maleated polyolefin as a compatibilizer for different polymers, mainly a modified polystyrene. It also does not teach the maleated polyproplene as enhancing the physical properties and allowing more flame retardant to be incorporated. Although U.S. Pat. No. 5,843,577, to Ouhadi et al. discloses a thermoplastic elastomer having improved surface properties due to the addition of, among other things, certain types of maleated polypropylenes, it also is distinguishable in that the maleated polypropylene is compatibilizing different materials and does not enhance physical properties that allow the incorporation of additional flame retardant.
The present invention has resulted from the discovery that a composition which comprises a major amount of a thermoplastic elastomer or a blend of thermoplastic elastomers having an average melt index of less than 6, a minor amount (i.e., less than 30% by weight) of polymeric elastomer, a maleated polypropylene, a flame retardant, and a filler material results in a thermoplastic elastomer film composition that has improved physical properties, processing, and flame retardancy while being useful for automotive interiors, wallcoverings, upholstery, advertising films or banners, and tenting. The composition is processable by calendering to make films having a thickness of less than 10 mils. The film can then be handled to be combined with other films or to be bonded to other support materials such as scrim fabrics.
The thermoplastic elastomer composition for use in automotive interiors, wallcoverings, upholstery, advertising banners, and tenting comprises a major amount of a thermoplastic elastomer or a blend of thermoplastic elastomers having an average melt index of less than 6, a minor amount of a a polymeric elastomer (i.e., less than 30% by weight), a maleated polypropylene, a flame retardant, and a filler material.
The thermoplastic elastomer (or xe2x80x9cTPExe2x80x9d) can be any copolymer of ethylene and a C3 to C8 olefin produced with a metallocene or Kaminsky catalyst (or xe2x80x9csingle sitexe2x80x9d) catalysts and having a molecular weight distribution (Mw/Mn) of less than or equal to 3 is contemplated for use as this component. Examples are copolymers of ethylene and butene, copolymers of ethylene and hexene and copolymers of ethylene and octene. It is preferred that the TPE is a mixture of TPE""s, where the TPE""s have different melt indexes with one being higher than the other, but with the weighted average melt index being less than 6, less than 3 and less than 2 being also preferred. Examples of TPEs are the Exact(copyright) polymers from Exxon Mobil Chemical. The TPE will be present in a majority amount of from 50% by weight to about 95% by weight based upon the weight of all of the polymers. Preferably, the TPE is more than 60% by weight, with more than 80% by weight being further preferred.
The xe2x80x9cpolymeric elastomerxe2x80x9d is a rubbery elastomer which will provide improved tear and elongation at break in the TPE composition and is preferred to be one of, but not limited to, a styrene-ethylene-butylene or xe2x80x9cSEBxe2x80x9d rubber with a Shore xe2x80x9cAxe2x80x9d hardness of 60 to 80, and a solution (25% weight in toluene viscosity of 6,000 to 9,000 CPS), a non-vulcanized chlorinated polyethylene with a chlorine content of between 30 and 42%, and a mooney viscosity (MS 1+4 121C) of between 42 and 94; and an (ethylene/vinyl acetate) copolymer or (ethylene/carbon monoxide) copolymer with a melt flow index of between 8 and 100 and a crystalline melt temperature of between 59 and 70xc2x0 C. Examples of polymeric elastomers are Kraton(D G-1650 thermoplastic rubber, which is a styrene-ethylene-butylene block copolymer, Elvaloy(copyright) HP511 resin from duPont, which is an ethylene vinyl acetate copolymer, and Tyrin 3615 from duPont Dow Elastomers, which is a chlorinated polyethylene. The polymeric elastomer will be present in a minor amount, about 1% to 30% by weight based upon the total weight of the polymers, preferably up to 20% by weight, with up to 10% by weight being further preferred.
The TPE composition of the present invention is achieved using processing equipment, which is typical for such materials. For example, in the preferred process, the ingredients will be weighed, pre-blended, mixed in a Banbury mixer, then passed through two 2-roll mills, a strainer extruder, and finally, calendered on an inverted xe2x80x9cLxe2x80x9d calender. There is no criticality in the equipment as long as it effectively mixes the composition and produces a thin film having an appropriate surface finish. It is preferred that the olefin thermoplastic elastomer composition for use in the present invention be prepared by blending together the components without the formation of crosslinking, from the viewpoint of formability at the final calendering and workability at lamination and/or vacuum forming.
For example, the thermoplastic elastomer composition can be prepared by preparing specified amounts of the ethylene/alpha-olefin copolymer elastomer and the polypropylene resin, charging them into an agitation mixer such as Henschel mixer (trade name), a supermixer or a tumbler mixer and effecting agitation blending generally for 1 to 10 min. In particular, while the use of the tumbler mixer takes about 10 min, the supermixer advantageously enables preparing the desired composition by agitation blending within about 3 min. According to necessity, the olefin thermoplastic elastomer composition can be melt kneaded by the use of a screw extruder or the like generally at 170xc2x0 C. to 250xc2x0 C., preferably, 210xc2x0 C. to 230xc2x0 C. and thereafter pellet
It may be desirable, on occasion, to employ a mineral oil in the present invention to improve not only the formability at calendering but also the capability of enhancing the mechanical properties of obtained shaped items suitable from the viewpoint of the hue and odor. In the selection of the mineral oil, the use of high-boiling-point oil fractions such as paraffinic, naphthenic, and aromatic mineral oils is preferred from the viewpoint of improving the formability. In this thermoplastic elastomer composition, the present invention, 0 to 30 parts by weight, preferably, 5 to 10 parts by weight of mineral oil is employed per 100 parts by weight of the thermoplastic elastomer composition, i.e., the total amount of the TPE, the polyolefin, and the polymeric elastomer.
The choice of the polymeric elastomer is dependent on the final physical properties desired, which can include tensile strength, % extensibility, flammability, and cold temperature performance. Modifications would need to be made to the formula to allow for processing differences. Chlorinated polyethylene, in particular, would have to be used with a reduced amount of paraffinic, napthenic and aromatic oil or excessive sticking to heated processing rolls would be encountered.
The maleated propylene functions as a compatibilizer for this composition. Its function is to improve the melt processing, physical properties and flame retardancy of the composition by increasing the amount of flame retardant that can be loaded into the composition. The preferred maleated polypropylene is a polypropylene homopolymer modified with maleic anhydride as a functional monomer. These are available from Uniroyal Chemical as Polybond(copyright) 3150 (melt flow rate of 509 g/10 min at 210xc2x0 C. and 2.16 kg) and 3200 (melt flow rate of 110 g/10 min at 190xc2x0 C. and 2.16 kg). The maleated polypropylene will be present in an amount of about 0.25% to about 5%. Amounts of 2% are preferred.
The flame retardant(s) to be employed in this invention include alumina trihydrate antimony trioxide, barium metaborate, decabromo diphenyl oxide, ethylene bis (tetrabromophthalimide), tetradecabromodiphenoxybenzene, ethylenebis (dibromonorbornanedi-carboximide), or any combination thereof. The combination of alumina trihydrate, barium metaborate and antimony trioxide is preferred, with the alumina trihydrate comprising the majority (i.e., more than 60% by weight) of the combination, and the barium metaborate and antimony trioxide comprising a minority (i.e., less than 30% by weight) for each, of the combination. Further, the combination can be employed with or without a bromine containing flame retardant, such as decabromo diphenyl oxide. The flame retardant will be present in an amount of about 15% to about 70%. Amounts of 45% are preferred.
The filler materials can be any of those normally used with film forming plastics. The thermoplastic elastomer composition of the present invention may be loaded with various additives and fillers in amounts not detrimental to the objects of the present invention. Examples of such other additives include antioxidants, antistatic agents, ultraviolet absorbers, age resistors and pigments. The filler will be present in an amount of about 5% to about 50% by weight based upon the weight of the polymers, i.e., the weight of the TPE plus the polyolefin plus the polymeric elastomer. Amounts of less than 40%, 30%, 20%, and 10% by weight are preferred.
The composition can include useful additives including for example, process stabilizers, antioxidants, ultraviolet absorbers, soap, such as metal soaps, anti-static agents, lubricants, nucleating agents, pigments, and dispersants for pigments.
In the calendering of the nonflammable olefin thermoplastic elastomer composition for use in making films in accordance with the present invention, the lubricant for use in the present invention imparts fluidity to the molten thermoplastic elastomer composition while maintaining a certain degree of compatibility therewith, so that the frictional resistance on the roll surface is reduced. This prevents the sticking of the composition to rolls and facilitates the forming of the composition. Examples of the lubricants exerting the above functions include higher paraffinic hydrocarbons; higher fatty acid compounds such as higher fatty acids, metal salts of higher fatty acid, higher fatty acid amides and alkyl esters of higher fatty acid (e.g., esters of higher fatty acids and aliphatic monohydric or polyhydric alcohols); higher aliphatic alcohols; polyethers; aromatic carboxylic acid compounds such as phthalic acid diamides and phthalic acid esters; diamine/carboxylic acid condensates; silicones (silicon resin); natural and synthetic rosin; and composite lubricants composed of at least two thereof. Specific examples of the above lubricants include paraffin wax, polyethylene wax, montan wax and hardened castor oil, such as the higher paraffinic hydrocarbon; stearic, palmitic, lauric and oleic acids as the higher fatty acid; magnesium, calcium, aluminum and zinc stearates as the metal salt of higher fatty acid; stearamide, oleamide, lauramide, ethylenebisstearamide, ethylenebislauramide and stearoleamide as the higher fatty acid amide; butyl stearate, ethylene glycol monostearate and glycerol distearate as the alkyl ester of higher fatty acid; stearyl, palmityl, oleyl and lauryl alcohols as the higher aliphatic alcohol; ethylene oxide/propylene oxide copolymer as the polyether; bis(2-ethylhexyl)phthalate as the phthalic acid ester; xylylenediamine/aliphatic carboxylic acid condensates (wax: for example, having approximately 1,000 of average molecular weight) as the diamine/carboxylic acid condensate; and polydimethylsiloxane as the silicone. These lubricants may be used either individually or in combination.
In the sheeting by calendering and postforming by vacuum forming, the use of a composition in which the amount of added lubricant is far smaller than 0.1 part by weight encounters the problem that excessive sticking of the composition to calender rolls occurs. On the other hand, when the amount of added lubricant is far larger than 3 parts by weight, problems are encountered. Not only does the lubricant migrate to the sheet surface during or after the forming with the result that winding of the composition around the calender rolls is often unsatisfactory during calendering, but also the produced sheet has poor coatability and/or a poor appearance.
A vital component to calendering films under 0.010 inches (0.25 mm) is having a wide processing window; a narrow processing window precludes the physical handling of film on the calender and calender train rolls; materials such as flexible and rigid PVC, ABS and various rubber compounds can all be readily calendered as they are classified as having an amorphous molecular structure and thus a wide processing window. Other polymers such as polystyrene, nylon, polyethylene, polypropylene, are classified as having a crystalline molecular structure and thus a narrow processing window. These types of polymers are processable by extrusion, injection molding and blow molding.
The key to the present invention is the choice of thermoplastic elastomer to simulate the processing window of flexible PVC. These unique materials allow the calendering of thin gauge films.